The longterm goal of this research program is to try to learn how fibrinogen works. We are interested in the underlying physiologic and pathologic processes involving fibrinogen in the control of hemorrhage and the development of thrombosis and atherosclerosis. Our research involves five specific series of experiments which are all correlated with important functional properties of fibrinogen: polymerization, crosslinking, degradation, and interactions with calcium, platelets, and fibronectin. (1) We will use congenital variants of fibrinogen and a human antibody to fibrinogen as probes to study the processes of polymerization. We will carry out fundamental studies on a fibrinogen variant, which is characterized by failure to release fibrinopeptide A and subsequent abnormal polymerization, in order to characterize the specific functional domains of fibrinogen involved in these reactions and to describe the biochemical defect. We will use light scattering and elastometry to study polymerization in these variants. (2) We propose to make chemically modified fibrinogen in which the modification is specifically directed to a polymerization domain. This will be done by carrying out the modification procedures on fibrinogen while it is bound to a fibrin monomer affinity matrix. This unique type of modification will help us to map out a specific polymerization domain. (3) We will study the interaction of calcium with fibrinogen and fibrin by measuring europium ion luminescence lifetimes. The advantage of this technique is that both liquid and solid samples (both coarse and fine gels) can be studied and directly compared. (4) We will study the interactions of platelets and fibrin which are important in clot retraction. We want to determine if a specific protein on the surface of activated platelets, such as fibrinectin, is a mediator of fibrin-platelet interactions. (5) We will make quantitative measurements on the effects of fibronectin on fibrin polymerization, crosslinking, elasticity, and degradation. All of the studies in this program are designed to learn more about the functionally important domains in fibrinogen.